The present invention relates to a bulb-shaped fluorescent lamp.
As shown in FIG. 6, a holder for use in a conventional fluorescent bulb is arranged such that a front face is flat at its central portion and formed with three holes 10a for receiving fluorescent tubes 1 (not shown) including, for example, three U-shaped tubes 1a interconnected in a manner to encompass the central portion.
The fluorescent tubes 1, shown in FIG. 7, are inserted in the hole 10a and then retained by the holder 10 with a silicone adhesive 8 injected from a rear side of the holder 10, as standing upright in encompassing relation to the central portion of the holder 10. Thus, a large amount of silicone adhesive 8 is used for filling a gap in the rear portion of the holder so that the fluorescent tubes 1 may be positively retained by the holder 10.
The holder 10 is formed of a polyethylene terephthalate resin containing glass filler. The continuous service temperature for this resin is defined to range from 150xc2x0 C. to 155xc2x0 C. inclusive (Japan: Electric Appliances Regulations, US: UL Standard).
However, the conventional fluorescent bulbs encounter a problem that heat builds up in a space encompassed by the fluorescent tubes 1 so that a portion of the holder 10 encompassed by the fluorescent tubes 1 or the central portion of the holder 10 is subject to serious temperature rise beyond the specified temperature (150xc2x0 C.-155xc2x0 C.). Consequently, the resin is decomposed to change the holder 10 in color and the product quality impaired.
The resin decomposition also decreases the resin strength so that the fluorescent tube 1 may slip off the holder 10. It is noted, however, that the fluorescent tubes 1 are normally connected to a starter circuit via a lead-in wire and therefore, even when slipped off the holder 10, the fluorescent tubes 1 are allowed to hang on the lead-in wire keeping the fluorescent tubes from free fall.
A large amount of silicone adhesive 8 is used for fixing the fluorescent tubes 1 to the holder 10. This leads not only to cost increase but also to significant decrease in assembly efficiency due to extended curing time.
In a case where such a lamp has a globe (not shown), heat from the lamp operation causes a large amount of low molecular siloxane to be released from the silicone adhesive 8 used in large quantity. The low molecular siloxane, in turn, will cloud the globe (not shown), resulting in extreme reduction of luminous flux or impaired product quality.
In view of the foregoing, it is an object of the invention to provide a less costly bulb-shaped fluorescent lamp with improved assembly efficiency which prevents the product quality impairment due to change in color of the holder or the slipping off of the fluorescent tube from the holder reduced in resin strength.
It is another object of the invention to provide a bulb-shaped fluorescent lamp adapted to reduce the clouding of the globe thereby preventing the extreme reduction of luminous flux or the impairment of product quality.
In accordance with the invention, a bulb-shaped fluorescent lamp comprises a set of fluorescent tubes, each tube being provided with filament coils at both ends thereof, a starter circuit for activating the fluorescent tubes, a holder for retaining the fluorescent tubes, and a case containing the starter circuit, wherein predetermined means is provided for lowering temperature at a portion of the holder encompassed by the fluorescent tubes.
Thus, the invention is designed to prevent the product quality from being impaired by the holder changed in color and the fluorescent tubes from slipping off the holder reduced in resin strength, as well as to accomplish improved assembly efficiency and cost reduction.